Not Applicable.
The present invention generally relates to the field of integrated optical waveguide devices controlled through optical phase, and in particular to hybrid MEMS/waveguide structures for phase shifting or polarization state changing.
A technology referred to as micro-machining and micro-electromechanics has emerged relatively recently as a result of advances in semiconductor technology, especially in the field of semiconductor processing. Micro-electromechanical devices are complex structures which individually include one or more electrical systems and one or more micro-mechanical systems. Micro-electromechanical systems (MEMS) are fabricated with MEM devices using many of the same fabrication techniques that have miniaturized electronic circuits and made mass production of silicon integrated circuit chips possible. Micro-electromechanical systems are typically made of silicon, polysilicon, silicon nitride and silicon dioxide on silicon wafers. Micro-electromechanical systems used with optical elements to provide optical functions are termed Micro-opto-electro-mechanical systems (MOEMS).
More specifically, utilizing fabrication techniques such as wet etching and photolithography, basic structures like grooves, holes, trenches, hemispheres, cantilevers, gears, and shafts, etc., can be built upon or within a silicon wafer. From these basic structures, a wide variety of micro-mechanical devices can be constructed. For example, among the numerous micro-electromechanical systems that have been successfully implemented are valves, springs, nozzles, printer heads, accelerometers, and chemical sensors. More complex devices, such as gas chromatographs, can be fabricated upon a silicon wafer a few centimeters in diameter.
Integrated waveguide technology is making major inroads as the technology of choice for many advanced optical applications due to the possibility of integrating many optical functions in a single device with good performance and reliability, scalable manufacturing, and potentially lower cost. However, this progress has been mainly in the area of fixed or xe2x80x9cpassivexe2x80x9d applications where optical routing is fixed by a property of the light, often the wavelength, and only the temperature of the optical circuit is controlled. At present, most prior art waveguide devices being used for dynamic and reconfigurable applications use optical phase shift to effect control and thermo-optic phase shifters as the controlling element. The most notable exceptions are those made in semiconductor materials, where carrier injection can be used, and lithium niobate (LiNbO3), which has a high electro-optic coefficient allowing direct control by means of an electric field.
For thermo-optic or carrier injection devices the drive power required to achieve the phase shift is quite high ( greater than 100 mW per element) and lithium niobate devices involve a costly material that is thermally unstable because of the pyroelectric effect. These are both severe impediments for use in integrated, high channel count applications.
For emerging applications, such as dynamic gain equalizers and configurable optical add/drops, a technology is required that combines the low propagation losses required for large area DWDM devices and low drive power actuators that can be fabricated in arrays without a significant increase in the size of the chip. The present invention can provide a new type of structure that meets these criteria by combining established waveguide technology with MEMS-based electrostatic actuators that require little drive power.
A well-known prior art device in this field consists of a waveguide/MEMS structure where a cantilevered beam supporting a waveguide is offset by bending the beam in order to introduce losses. This structure is used for amplitude modulation rather than phase modulation and has the disadvantage that the light has to propagate through an air gap which would have to be AR (anti-reflection) coated. It has also been proposed to use the refractive index modulation due to the strain induced by electrostatically deflecting a cantilever containing a waveguide, to control an optical interferometer. However, in the interferometers considered, birefringence arising from the strain has not been used. Thus, it is desirable to use the birefringence induced by stress.
In accordance with the invention there is provided a controllable waveguide structure that combines waveguide and MEMS processing to produce electrostatically actuated, torsional stress-inducing phase shifters.
In accordance with the invention there is provided a controllable waveguide structure that combines waveguide and MEMS processing to produce electrostatically actuated, beam deflection stress-inducing birefringence shifters.
In accordance with the invention, there is further provided, a phase shifter for shifting a phase of an optical signal comprising a waveguide having a waveguiding region for guiding the optical signal therethrough; a substrate for supporting said waveguide; and means for inducing stress on the waveguiding region for shifting the phase of the optical signal. In accordance with an embodiment of the invention, the means for inducing stress are MEMS means.
In accordance with the invention, there is further provided, a polarisation state modifier for changing a polarization state of an optical signal comprising a waveguide having a waveguiding region for guiding the optical signal therethrough; a substrate for supporting said waveguide; and means for inducing stress on the waveguiding region for changing the polarization state of the optical signal. In accordance with an embodiment of the invention, the means for inducing stress are MEMS means.
In accordance with another aspect of the invention, there is provided, a method of inducing a phase shift of an optical signal propagating through an optical waveguide relative to the phase of another optical signal, comprising the steps of: supporting said optical waveguide on a substrate; providing MEMS means on said substrate; and inducing stress on the optical waveguide using the MEMS means for changing a refractive index of the waveguide and thereby shifting the phase of the optical signal propagating through said optical waveguide.
In accordance with another aspect of the invention, there is provided, a method of inducing a shift of the polarisation state of an optical signal propagating through an optical waveguide, comprising the steps of supporting said optical waveguide on a substrate; providing MEMS means on said substrate; and inducing stress on the optical waveguide using the MEMS means for changing a birefringence of the waveguide and thereby changing the polarization state of the optical signal propagating through said optical waveguide.
In accordance with the invention there is further provided an integrated micro-opto-mechanical system comprising a waveguide; a substrate for supporting said waveguide; and MEMS means for inducing stress on said waveguide for changing a refractive index of said waveguide, and an optical waveguide device influenced by the refractive index of said waveguide.
In accordance with the invention there is provided an integrated micro-opto-mechanical system comprising a waveguide, a substrate for supporting said waveguide and MEMS means for inducing stress on said waveguide for changing a birefringence of said waveguide, and an optical waveguide device influenced by birefringence of said waveguide.
The invention further provides a method for making a controllable waveguide structure that combines waveguide and MEMS processing for producing stress-induced changes of refractive index for phase shifting.
In accordance with the invention the MEMS means for inducing stress generates compressive stress in the waveguide.
In accordance with the invention the MEMS means for inducing stress generates tensile stress in the waveguide.
In accordance with the invention the MEMS means for inducing stress generates shear stress in the waveguide.
In accordance with an embodiment of the present invention a deformable membrane with a waveguide bridge crossing over top is provided with electrostatic actuation means to induce stress by deflecting the waveguide bridge to generate a change in the birefringence of the waveguide.
In accordance with an embodiment of the present invention a deformable membrane with a waveguide bridge crossing over top is provided with electrostatic actuation means to induce stress by twisting the waveguide bridge to generate a change in the refractive index or birefringence of the waveguide.
In accordance with an embodiment of the present invention, the birefringence is compensated for by using a reflective structure with a quarter wave plate to have opposite polarization states on forward and reverse passes to cancel the birefringence.
In accordance with the invention the waveguide is disposed asymmetrically in the cross section of the stressed member.
In accordance with the invention the waveguide is laterally displaced from an axis of symmetry of the stressed member.
In accordance with an embodiment of the present invention, mechanical stress is applied to a waveguide to generate strain which results in refractive index changes due to the elasto-optic effect.
In accordance with an embodiment of the present invention, mechanical stress is applied to a waveguide by electrostatic means.